Climate change may have a more unpredictable effect on the distribution of cold-blooded animals than scientists had previously thought, a new analysis shows.

Marine biologist Dr Amanda Bates and colleagues set out to explore how global warming will affect the distribution of animals such as fish, frogs and lizards.

"Although people had assumed that the ranges of species are limited by temperature, this was a paradigm that had not been tested at a global scale," says Bates, who worked on this study from Deakin University and the University of Tasmania.

In a new analysis published in the journal Nature Climate Change, Bates and colleagues from Simon Fraser University in Canada report that things are not as simple as that assumption might suggest.

The researchers first looked at existing data on what temperature ranges 142 different animal species could live within. They then compared those findings with the actual temperature ranges found where those species exist in the wild.

"We wanted to understand the window that animals can live within—both hot and cold," Bates says. "And then we asked whether those limits matched where they were found in nature.

Not filling their real estate

For cold-blooded animals living in the oceans, it turned out that the lab measurements and the real-world distribution patterns matched closely.

But the correlation was not so good on land. The researchers found that terrestrial cold-blooded animals did not live as close to warmer equatorial regions as the laboratory research suggested they could.

There are probably many reasons for this tendency, the researchers say. One of those factors is likely to be low rainfall in the hotter regions.

Surprises ahead

Looking to the future, the findings suggest that animals in the ocean and on land will respond differently as the climate warms.

In the oceans, the researchers predict that animals such as fish will tend to move away from the equator in a relatively orderly way. On land, they predict that animals would have a more chaotic response.

In fact, when the researchers collected 648 examples of climate-induced range shifts that have occurred around the world, both on land and in the sea, they found that this was indeed happening.

As cooler areas warmed, the animals on land have tended to move into newly comfortable regions. But they do not leave the warmer areas behind.

"On land, we're going to find that animals' ranges will stretch," says Bates. "That means that you're going to mix species up with animals they've never seen before. We're going to have some surprises."

"We still don't have a clear picture of why animals live where they do on our planet," she says. "That's information we're going to need if we want to manage the effects of climate change on species distribution."